You can find the LTE Diagnostics at Diagnostics → LTE.
Here you can see the current settings and status of your LTE setup.
To change your LTE setup please go to the Interface page of your LTE at Interfaces.
System Status shows you the current status of the LTE modem.
SIM Status shows the status of the SIM card and if it is locked.
Channel Rates shows the theoretical maximum speed and the speed the LTE modem negotiated with your provider.
Packet shows the statistics about the current open LTE connection.